A significant problem which arises in the manufacturing of opto-electronic modules such as receivers, transmitters and transceivers relates to the assembly of the modules onto circuit boards. The problem is attributable to the fact that many high-speed opto-electronic modules utilize direct attachment of a single-mode or other type of optical fiber to internal components in order to maximize the amount of optical signal power coupled to or from the fiber within the module package. Modules in which internal optical fibers extend from the package for external connection with a circuit board are generally referred to as "pig-tailed" modules. The fibers extending outside the package are generally very fragile, and the module therefore cannot be installed on a circuit board using automated assembly processes. Instead, great care must be taken during the board-level installation process to avoid subjecting the fibers extending from the package to a tight bend or other stressful condition. A manual assembly process is often used to install the module onto the circuit board. After the module package is soldered, epoxied or otherwise secured in place on the board, an operator very carefully winds or secures the excess external fiber on spools or other structures which are also mounted on the board. This is not only a labor-intensive and time-consuming process, but is also a primary cause of fiber breaks which can render the module unusable.
Some prior art opto-electronic modules avoid the board-level fiber management problems associated with pig-tailed modules by utilizing a "connectorized" package in which optical fibers do not extend from the package. In fact, conventional connectorized packages generally do not utilize any internal fiber connections. This is due in part to the fact that the arrangement of a fiber adjacent to an internal interface of the connector may lead to undesirable reflection at the interface as well as other stability problems. Instead, conventional connectorized packages may be configured with an optical detector or optical signal source adjacent to the internal connector interface, such that light is coupled directly to or from the connector interface via lenses or other types of optics. However, the coupling efficiency of modules configured in this manner is generally inferior to that of the pig-tailed modules. Devices which require an optimal coupled optical power, and thus an internal fiber connection, are generally required to utilize a pig-tailed package instead of a connectorized package, and will thus be susceptible to the above-described fiber management problems at board-level assembly.
If the opto-electronic module is a transceiver, that is, a device incorporating both an optical transmitter and an optical receiver in a common package, it may require the fiber pig-tail connection only for the transmitter output. This is due to the fact that the active area of the positive-intrinsic-negative (PIN) diode detector or avalanche photodiode (APD) detector used in the receiver is typically very large, on the order of 75 .mu.m in diameter. Therefore, the enhanced coupling provided by the fiber pig-tail connection may be unnecessary in the receiver. Although many opto-electronic modules include a multimode fiber, having a core diameter on the order of 50 to 100 .mu.m, attached to the receiver detector, this fiber pig-tail connection is often not required. The most significant aspect of the internal fiber connection problem in a transceiver thus often relates to managing the single-mode fiber pig-tail connection to the laser or other transmitter optical source.
FIGS. 1 and 2 illustrate conventional opto-electronic transceiver module packages. FIG. 1 shows a connectorized optical transceiver module 10. The module 10 includes a package 12, an input or receive optical connector 14 and an output or transmit optical connector 16. The package 12 is illustrative of the type of package used in Part No. HFBR 5205T from Hitachi. The receive connector 14 is configured for attachment to a mating connector of an optical fiber on a circuit board, such that an input optical signal may be supplied to an optical receiver in the package housing 12. The receiver portion of the module 10 includes receiver electronics 18, a submount 20 and a PIN diode or APD detector 22 attached to the submount 20. The detector 22 converts the input optical signal into an electrical signal which is processed in receiver electronics 18. The transmit connector 16 is also configured for attachment to a mating connector of an optical fiber on a circuit board, such that an output optical signal generated by a transmitter in the package housing 12 may be supplied to the circuit board. The transmitter portion of the module 10 includes transmitter electronics 24, a submount 26 and an optical source 28 attached to the submount 26. The optical source 28 may be, for example, a Fabry-Perot laser or a laser diode. The optical source 28 generates an output optical signal which is modulated by a data stream or other electrical signal supplied to the optical source 28 from the transmitter electronics 24. The connectorized module 10 may be about 1 inch in width, 2 inches in length and 1/2 inch in thickness. As noted above, the conventional connectorized package of FIG. 1 is generally unable to utilize internal fiber connections. The connectorized package therefore does not provide optimal coupling of optical signal power in and out of the module 10, due to connector and mating losses, interface reflections and other instabilities.
FIG. 2 shows a typical pig-tailed transceiver module 30, with a package 32 illustrative of the type used in Part No. MF-156DS-TR124-002/003 from Mitsubishi Electric and Part No. TRV5366 from Hitachi. The module 30 includes a transmit output 36 supporting a pig-tailed transmit optical fiber 38, and a receive input 40 supporting a pig-tailed receive optical fiber 42. The transmit output and receive input are arranged on the same side of the package 32. The package 32 may be on the order of about 3 inches wide by 4 inches long by 1/2 inch thick. The fiber 42 is an input multi-mode fiber which supplies an input optical signal to a receiver in the module 30, and the fiber 38 is an output single-mode optical fiber which carries an output optical signal generated by a transmitter laser or other optical source in the module 30. As noted above, one or both of the single-mode optical fiber 38 and the input multi-mode fiber 42 may be configured using a direct fiber connection to an internal submount. The pig-tailed fiber is secured in a V-shaped pregroove formed in the submount to facilitate the placement of the fiber relative to the optical source. Although the package output 36 and package input 40 provide some support for the fibers 38 and 42 extending from the package 32, this support is insufficient to prevent the board-level fiber management problems described above and the resulting increased likelihood of damage to the internal fiber connections. The pig-tailed module 30 avoids the connector and mating losses and other instabilities associated with the connectorized module 10, but substantially increases the costs and risks associated with board-level assembly.
It is therefore apparent that a need exists for improved techniques for packaging optical modules, such that internal fiber connections can be utilized without the increased manufacturing cost, decreased reliability and other problems associated with conventional connectorized or pig-tailed packages.